The present invention relates to a narrow track thin film magnetic head and a magnetic disk apparatus carrying the thin film magnetic head and more particularly to the structure of a recording head of the thin film magnetic head.
The thin film magnetic head carried on a high recording density magnetic disk apparatus has been used widely and many proposals to improve the performance have been made. Recently, there is an increasing demand for improvement in the performance directed to high density recording and today, a composite apparatus in which the conventional inductive type recording head and the reproduction head such as highly sensitive MR head are separately incorporated tends to be used generally. The performance of recording and reproduction has been improved remarkably by the aforementioned composite apparatus having the separated heads as well known in the art but from the standpoint of further promotion of improvement in the performance, only the improvement in the MR head or GMR head directed to high sensitivity is insufficient and improvements in the structure of the recording head are particularly important as disclosed in JP-A-08-249614 (corresponding to U.S. Ser. No. 399781 filed on Mar. 6, 1995) making a proposal to promote the performance by improving the structure of the recording head.
An expedient such as improving the track density or narrowing the track width occupies a factor in increasing the recording density. The expedient is, however, accompanied by problems that a recording magnetic field from the tip of a magnetic gap decreases and magnetic flux is concentrated to opposite ends of track width, leading to magnetic saturation at the opposite ends. To meet demands for the expedient, therefore, it is necessary to show a way to suppress the decrease in recording magnetic field, to suppress the magnetic saturation at the opposite ends of width of a narrow track width so as to reduce the amount of a side-fringing onto a recording medium (the side-fringing is a unwanted spreading of recording pattern caused when information is recorded in excess of the track width in the track width direction as a result of concentration of the magnetic flux to the opposite ends) and to assure a necessary recording magnetic field satisfactorily.
The aforementioned JP-A-08-249614 discloses a proposal to improve recording magnetic field vs recording current characteristics and addresses magnetic saturation in the magnetic yoke, as in the present invention. To describe in greater detail, JP-A-08-249614 discloses a technical idea that in a magnetic yoke shaped to have a width which starts to greatly diverge or spread at a position (flare point) between the magnetic pole tip and a rear portion of the magnetic yoke, the width is gradually spread or increased toward the flare point, starting at a position (zero throat point) which is closer to the magnetic pole tip than the flare point and at which the magnetic gap terminates, in order to cause magnetic saturation to take place substantially simultaneously over a length of the magnetic yoke between the zero throat point and the flare point.
However, the above prior art does not take into consideration problems raised in narrowing the track, failing to refer to magnetic saturation at opposite ends of track width and problems encountered in connection with magnetic saturation at the magnetic pole tip.
An object of the present invention is to provide a thin film magnetic head having a recording head which can suppress magnetic saturation at opposite ends of the width of a narrow track width to reduce the amount of the side-fringing onto a recording medium and which can assure a necessary recording magnetic field satisfactorily and to provide a magnetic disk apparatus carrying the magnetic head.
To accomplish the above object, a thin film magnetic head according to one aspect of the present invention comprises:
a first magnetic yoke having a first magnetic pole facing a magnetic recording medium;
a second magnetic yoke having a second magnetic pole so disposed as to define a magnetic gap between the second magnetic pole and the first magnetic pole and forming at its rear portion a magnetic circuit which magnetically short-circuits to the first magnetic yoke;
a conductor coil formed between the first and second magnetic yokes; and
an insulating layer for insulating the conductor coil from the first and second magnetic yokes,
wherein the second magnetic yoke has a magnetic gap depth (GD) over which the spacing of the magnetic gap defined between the first and second magnetic yokes keeps substantially equal toward the rear portion of the second magnetic yoke, starting at the tip of the second magnetic pole and the spacing between the first and second magnetic yokes is increased toward the rear portion, starting at a position corresponding to the magnetic gap depth extending from the second magnetic pole tip, to house the conductor coil and the insulating layer;
the second magnetic pole of the second magnetic yoke has a width (TW) in the track direction for recording a signal on a track width of the recording medium;
the width (TW) keeps constant over a predetermined length (PH) toward the rear portion, starting at the second magnetic pole tip and spreads monotonically toward the rear, starting at a spread start position corresponding to the predetermined length (PH) from the second magnetic pole tip; and
the predetermined length (PH) terminating in the spread start position of the width (TW) of the second magnetic yoke is shorter than the magnetic gap depth (GD)